Development of Multispecies Models of Fish Community Dynamics on Georges Bank

William T. Stockhausen

Michael J. Fogarty

Northeast Fisheries Science CenterNOAA FisheriesWoods Hole, MA

Patterns of Fish Abundance on Georges Bank

Year

1965 1970 1975 1980 1985 1990 1995 2000

mea

n w

t. p

er t

ow

(kg

)

1

10

100

FlatfishGadids Other groundfish Pelagics Skates Total

Approach to Modeling

• Construct energy flow models– Network analysis– Static picture: assumed equilibrium, linear processes– Underlying dynamic processes recognized

• Different time periods ↔Different environmental conditions

• Develop dynamic models– Represent change in the system– Accommodate nonlinear processes– Focus on components:

• Take advantage of differences in connectivity within/between trophic levels

Overlapping Data Requirements

• Dynamic models: time series of – Abundance (biomass) for each species

– Catch (biomass) for each species

• Energy flow models: estimates of– Average production for species groups

• Prod = Time-averaged biomass x P/B

– Averaged consumption for species groups• Cons = Time-averaged biomass x C/B

– Average total harvest for species groups

Multispecies Production Models for the Fish Community

• Develop multispecies production models for the fish community

• Primary objective is to test for species interactions

• Model incorporates– Competitive interactions– Predator-prey interactions (Type I functional response)

• Parameter estimation will be done in a Bayesian context (using WinBUGS)

ts

Br

tsts CeBB jtjjss

,

1

,1,

,,

Initial Multispecies Matrix

Cod HaddockSilver Hake

Yellowtail Flounder

Winter Flounder

Winter Skate

Little Skate

Herring Mackerel

CodPred

CompComp Pred Pred

Haddock Comp Comp Comp Comp

Silver Hake

Comp Pred Pred

Yellowtail Flounder

Comp Comp Comp Comp

Winter Flounder

Comp Comp Comp Comp

Winter Skate

Comp Comp Comp Comp Comp Pred Pred

Little Skate

Comp Comp Comp Comp

Herring Prey Prey Prey Comp

Mackerel Prey Prey Prey Comp

Stock Assessment Biomass

Year

1965 1970 1975 1980 1985 1990 1995 2000

Bio

mas

s (M

T x

10-3

)

1

10

100

1000

Haddock Atlantic Cod Yellowtail flounder

Estimating Biomass Time Series

Estimating Biomass Time Series

• Results from stock assessments generally inappropriate– Spatial coverage

– Temporal coverage

– Not available for all species

Estimating Biomass Time Series:NEFSC Bottom Trawl Survey Data

• 40 year dataset

• Semiannual surveys (Spring, Fall)

• Cape Hatteras to Gulf of Maine

• Nearshore to continental shelf break

• Stratified random survey design

• Standardized gear, procedures

Estimating Biomass Time Series:Survey Strata

Estimating Biomass Time Series:Survey Indices

Spring Survey Indices

Year

1970 1975 1980 1985 1990 1995 2000

mea

n c

atch

per

to

w (

kg)

1

10

100Haddock Atlantic Cod Yellowtail flounder

Estimating Biomass Time Series:Issues with using trawl survey data

• Unequal catchabilities among species

• High sampling variability

Adjusting for Catchabilities

• Species-specific catchability factors based on – Published literature

• Visual observations and acoustic measurements

• Comparisons between survey and assessment results

• Meta-analysis of assessment-based catchabilities

– Analysis of trawl survey data• Day/night correction factor for individual

net tows

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ss

ss

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ecq

cq

q

CaAB

1ˆ

ˆ

ˆˆ

,

,

,

,,,,

Smoothing Survey Biomasses

• Model observation error as uncorrelated multiplicative noise

• Assume observed and underlying processes can be characterized by ARIMA models

• Smoothed results based on

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)()()()(

)()()()()(

;

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BBBUB

BUBBOB

UO

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,,ˆ

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),(),(},{

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Smoothed Biomass Time Series

Atlantic Cod Biomass

Year

1970 1975 1980 1985 1990 1995 2000

Bio

mas

s (M

T x

10-3

)

10

100

Spring trawl surveyARIMA-smoothed resultsAssessment biomass

Smoothed Biomass Time Series

Haddock Biomass

Year

1965 1970 1975 1980 1985 1990 1995 2000

Bio

mas

s (M

T x

10-3

)

10

100

Spring trawl surveyARIMA-smoothed resultsAssessment biomass

Estimates of Production and ConsumptionFor the Energy Flow Models

Production

1960's 1970's 1980's 1990's

Pro

du

ctio

n (

kcal

m-2

yr-1

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Atlantic codHaddock

Consumption

Time Period

1960's 1970's 1980's 1990's

Co

nsu

mp

tio

n (

kcal

m-2

yr-1

)

0

2

4

6

8

10

12

Summary

• Multspecies production models will provide dynamic counterpoints to static, equilibrium-based energy flow models

• Procedures developed for estimating time series of species biomass from NEFSC Bottom Trawl Survey data– provide biomass time series for the production models– provide production/consumption estimates for energy flow

models